Engineering Considerations for Staple System Awnings

Staple System Awnings

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Staple System Awnings can utilize any type of fabric and be manufactured in almost any design allowing total product flexibility. They are considered to be a manufacturer friendly awning system because the fabric cover does not have to be manufactured with exacting precision so it fits an existing fixed frame. Rather fabric can be cut from the roll, stapled into the channel of the framework, excess fabric trimmed and PVC insert applied. These awnings are typically manufactured and delivered to the job site with the covers fitted. Because the covers are already attached to the frame at installation, Z Brackets are used for mounting and can be located anywhere on the awning where framework touches the wall.

Although Staple System Awnings are manufacturer friendly, they are not always considered to be building code friendly and can be an issue in areas where cover removal for extreme wind or snow conditions are necessary. Once the cover is removed (cut away), new fabric must then be installed due to the inherent design of the framework.

Most staple system extrusions are available in sizes as small as 1”x1” and as large as 2”x2”. The base metals are either aluminum or galvanized steel. The shapes in which the extrusions are available in may differ slightly from one supplier to another but remain the same in concept. Extrusions with a flange are typically used at the bottom of the awning to support egg crating which allows the awning to breathe, light the be transmitted at night and keeps bird from making nests inside the awning. Below are some examples of staple system extrusions:

Because staple system awnings are considered to be permanent structures, they must adhere to federal, state and local building codes. The loads for which awnings must be designed to meet can be generalized as follows*:

Dead Load

This is the self-weight of the awning or canopy frame, fabric and hardware. This load must always be included with other design loads since it is always acting on the structure. For instance, if one were designing an awning for 20 psf snow load, and the structure weighed 2 psf, then the design should actually account for 22 psf total load.*

Wind Load

Speed or Velocity Basic wind pressure is a function of its speed and can be computed as the product of 0.00256 x V ^2. It can be readily observed then, for example, that the wind forces on an awning are four times greater if the wind speed is doubled, and the forces are nine times greater if the wind speed is tripled. Design wind speeds are generally shown on maps published in the building code as local codes may require higher design wind speeds.http://www.windspeedbyzip.com/ is a free online tool for professionals to easily determine the 3-second gust basic windspeed for any location in the continental United States.*

Exposure

Exposure is a general category for the amount of protection from the wind that is afforded by the surrounding environment. Structures located in wooded areas, for instance, do not have to be designed for as much wind force as a structure located in an open area.

Gusts

Gusts is a sudden, brief increase in speed of the wind. www.windspeedbyzip.com is a free online tool for professionals to easily determine the 3-second gust basic windspeed for any location in the continental United States.*

Drag and Uplift

Drag is the wind-induced pressure toward the fabric surface, and uplift is the pressure away from the fabric surface. Wind forces on an awning system act in different directions (toward or away from the fabric surface depending on a variety of factors). When designing an awning frame, all these factors must be taken into account. Because awnings can be designed in so many different shapes and sizes, uplift can be figured anywhere between 12-26 pounds psf for most applications.*

Return Period

This term is used to describe the time interval which is the basis for establishing the required design wind speed. For most applications the return period is 50 years. This simply means that the required design wind speed is that which has a 0.02 statistical probability of occurring once in 50 years. Loss and safety experts have determined that it is an acceptable level of risk and have based code design requirements on it.

*The information provided is simply a generalization to demonstrate the terms as they are listed and should never be used in any calculations for any project.

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